Liverpool have completed the £20m signing of winger Lazar Markovic from Benfica on a "long-term deal".

The 20-year-old helped Benfica win the Portuguese title last season after joining the club from Partizan Belgrade in the summer of 2013.

"I hope that I will fulfil the expectations of the supporters, coaches, players and all connected to the club," he told Liverpool's website.

The Serbia international becomes the club's fourth signing this summer.

Analysis: European football writer Andy Brassell

"He's a player with a rare talent. The raw potential is absolutely enormous. If he can progress at the present rate he's going to be worth twice the money that they paid for him in 12 to 18 months' time, so it's a good investment."

If he decides to move to Merseyside, he could cost the Reds £10m with add-ons but will return to Lille on loan for the 2014-15 campaign.

Liverpool, who are selling striker Luis Suarez to Barcelona for £75m, are attempting to strengthen their squad as they prepare to compete in the Champions League for the first time since 2009 after their second-placed finish in the Premier League last season.